The hematologic support of cancer and aplastic anemia patients is studied. A preclinical canine model has permitted determination of the dose of nucleated cells and CFUc in marrow or peripheral blood which is required to rescue dosg from the lethal effects of total body irradiation, and is being used to study compounds (e.g., dextran sulfate) which increase the levels of CFUc in the peripheral blood. The role of autologous reconstitution by marrow or peripheral stem cells is studied in a variety of patients with refractory neoplasms receiving "ablative" chemotherapy. Assays for stem cell reserve in cancer patients under therapy are developed and studied. With respect to granulocyte transfusion, colchicine has been shown to protect cells collected by filtration leukapheresis from human donors. Retrospective analysis of over 1000 platelet transfusions in aplastic anemia patients has revealed the frequent inadequacy of HLA typing as a compatibility system. The capillary platelet migration inhibition assay has been shown to be a useful adjunct to HLA in selection of compatible donors for highly alloimmunized recipients. A clinical trial to define which cancer patients require HLA-matched platelet transfusions for optimal support is underway.